Iron has a crucial role in biology; thus, alterations from homeostatic levels of iron, either high or low, are detrimental to health. Commonly occurring diseases that involve aberrant iron homeostasis include chronic hemochromatosis and thalassaemia in which excess iron accumulation leads to iron deposits in heart and liver. Abnormally high iron levels in the brain correlate with a number of neurological disorders including Alzheimer's, Huntington's chorea, Friedreich's ataxia, Parkinson's disease and multiple sclerosis. For example, a hallmark of patients with Parkinson's disease is increased iron content in glial cells and dopaminergic neurons. In these diseases, excess iron may have a role in the progressive deterioration observed in patients. In addition, brain micro-bleeds lead to the deposit of excess iron. Such microbleeds have been attributed as one of the causes of dementia including Alzheimer's. It has been estimated that more than 5% of the population over 65 has either Parkinson's or Alzheimer's disease.
Clinical trials are underway to give patients chelating ligands to treat neurological disorders. There is a critical need for in vivo sensors that would track the effect of chelating drugs on brain iron levels. Iron levels in different areas of the brain may be diagnostic of neurological disorders.
MRI is the method of choice for monitoring high levels of iron in organs. Excess iron deposits are detected in organs such as heart, liver and brain by using MRI techniques that capitalize on differences in bulk water proton relaxivity in tissues that contain excess iron. This includes magnetic susceptibility imaging, and T2 and T1 weighted MR images. These methods, however, suffer from artifacts such as areas of calcification that can complicate interpretation. More direct imaging methods are needed that would register both the iron oxidation state and distribution in tissue. New methods for the detection and imaging of specific iron species may open up new avenues of research on human diseases that involve iron mismanagement.